Lapping machine



Oct. 20, 1953 T. a; Lewis LAPPING MACHINE 4 Sheetg-Sheet l mm an mm Q 9wFiled May 22, I950 {I an QM ThomasGLewis ATTQRNEY T. G. aims 2,655,769

Get. 20, 1953 I MACHINE 4 Sheets-Sheet 2 Filed May 22, 1950 rm z ThomasG.Lewis ATTORNEY INVENTOR.

Oct. 20, 1953 'TJG. LEWIS LAPPING MACHINE 4 Sheets-Sheet 3 Filed May 22,1950 INVENTOR. Thomas G. Lewis ATTORNE Y Patented Oct. 20, 1953 UNITEDSTATES the? OFFECE LAPPING MACHINE Application May 22, 1950, Serial N0.163,561

17 Claims.

This invention relates to machines for lapping metal articles withsuspensions of particulate abrasives in liquid vehicles, andparticularly to an improved machine for the lapping of cylindricalshaped articles.

Previously, it has been the practice to employ lapping tools having arelatively high inherent retentivity for the abrasive materials whenlapping metal articles with abrasives suspended in liquids. Under theseconditions, a large proportion of the abrasive particles become embeddedin the laps, where they effect their abrading action on the work by ashearing or tearing motion somewhat resembling that of a conventionallathe tool. A varying quantity of the abrasive remains in a more or lessfree condition for one or more transverses of the tool past the workand, therefore, a non-uniform movement of the particles ensues,resulting in an uneven distribution of the abrading burden among theparticles, and scratching of the surface of the work. In addition,particles of surface material removed from the work in the course ofabrading tend to aglomerate into larger masses, which eventually defacethe work surface as lapping continues.

I have now found that an improved abrading action is secured when theabrasiv particles are rolled freely between the Working surface of thelapping tool and the Worked surface of the article being processed asrelative movement is maintained between the lap and the work. Thisrolling movement of the abrasive particles is depend ent on a number offactors, including the physical properties of the lamp material itself,the pressure with which the abrasive is forced into contact with thework, the viscosity of the liquid ve hicle in which the abrasive issuspended, the pattern of movement preserved between the lap and thework, and other variables. 1

An object of this invention is to provide an improved lapping machin forcylindrical objects which is capable of imparting a superior surfacefinish to the work with accompanying economies in time and labor.

Another object of this invention is to provide an improved lappingmachine for cylindrical objects which is largely automatic in operationand which may be attended by unskilled personnel.

Another object of this invention is to provide an improved lappingmachine for cylindrical objects which is capable of reproducing apredetermined quality of surface finish to a high degree.

These and other objects of this invention will become apparent from thedescription of the'following illustrative drawings in which:

Figure 1 is a side elevation of one embodiment of this machine employedfor the surface finishing of a relatively large diameter cylindricalroll, such as those used for the casting of film-forming materials;

Figure 2 is a front end elevation of the machine shown in Figure 1 withthe driving motor and driving belts for the lapping head shown by brokenline representation;

Figure 3 is a front elevation of the lapping head,

Figure 4 is a longitudinal section through the double eccentric drivingmechanism for the lapping head, with a rough lapping head attached,

Figure 5 is a fragmentary front end view of the double eccentric drivingassembly shown in Figure 4,

Figure 6 is a vertical central section through a lapping head employedfor fine lapping,

Figure 7 is a partially fragmentary perspective View of a rough lappinghead, and

Figure 8 is a perspective View of a lapping head employed for the finelapping operation.

In general, the objects 'of this invention are attained by providing anapparatus for rotatab-ly supporting the work and forcing particulateabrasives suspended in oil applied to the work. 7

against the surface with a self-aligning tool shaped to conform to thesurface, while maintaining ahigh degree of-random movement between theworking' surface of the tool-and the worked surface of the piecetreated. According to a specific embodiment of the in vention, theseobjects are accomplished by flexibly supporting a lapping head inparallel relation to the rotatably supported work, with resilient forceapplying means bearing against the lapping head, comprising a doubleeccentric (e. 23 and All) and self-aligning bearing rods (e. 42, 42)mounted in parallel relation with the double eccentric, thus formingthree principal reference axes so as to produce substantially free,threedimensional movement of the lapping head while still retaining thelongitudinal surfacing elements of the lapping head parallel to the axisof rotation of the cylindrical object being surfaced.

Referring to Figure 1, the apparatus comprises a base structure Iconsisting of a heavy I-beam frame resting on the building floor, whichframe is preferably strengthened by one or more cross pieces 2 welded tothe insides of the webs. To the top of frame I are secured sub-frames 3and 4, which may also be conveniently fabricated from channel irons orI-beams, sub-frame 3 providing support for th lapping head whilesub-frames 4 support a pair of self-aligning split pillow blockbearingspone-oi which is indicated at-5. Sub- =3 frames 3 and 4 areassembled upon base I with bolts 6 and 7, respectively. Bearings areassembled upon sub-frame 4 with bolts 8.

The cylindrical work piece 9, the integral annular shell ill of which isto be surfaced, is fixedly secured to shaft H by keys or other means andshaft I I is journaled in bearings 5, sufficient lateral clearancebetween the I-beams constituting the side members of base i beingallowed so that cylinder 8 is freely rotatable within bearings The upperflanges of base members I are provided with a series of drilled holes topermit adjustment of sub-frames 4 at var ing distances from the lappinghead to accommodate work of different diameters. Pinion l2 driven byshaft I3 connected to a suitable gear head motor, not. shown, turnsshaft 5! by engagement with bull gear is keyed to H at one end, rotationbeing in a counterclockwise direction as indicated by the arrow. tweenthe surface to be worked and the lap should not exceed about 180ft./minute for rough lapping about 175 ft./minute for fine lapping,therefore, cylinder 9 is revolved at a slow speed. In a typical casewhere a roll 24" in diameter with a face 24" wide as processed, a roughlapping speed of 1.6 R. P. M. and a fine lapping speed of 2.0 R. P. M.were entirely satisfactory.

As shown in Figures 1 and 2, sub-frame 3 supports uprights l5 carryingflanges at their lower ends for the reception of bolts l6 passingthrough drilled holes in the upper flanges of 3. The forward edge of theflange of sub-frame 3 is provided with strip I! securely welded theretowhich is drilled and tapped across its length for the rcg2;

thereto for the support of the front and rear bearings 2| and 22,respectively, which carry the outer shaft 23 of the double eccentricwhich drives the lapping head 24. Bearings 2i and 22 are preferably ofthe one piece pillow block type, incorporating integral shaft lockingelements, and are secured to pad by bolts 25.

The upper ends of uprights l5 are provided with hearing boxes 25,secured theretoby bolts 21, within which freely rotatable shaft 28 isjournaled. The central portion of shaft 28 is enlarged to a square crosssection as indicated at 29 for the reception of the forked ends of thetwo hanger arms 30 which are fixedly secured thereto. Attachment isaccomplished by rear plates 3| which complete the enclosure of portion29 when assembled to the forked ends of hanger arms 3!! withhexagonal-headed bolts 32 engaging with tapped holes in the hangers. Theforward ends of hangers 30 are provided with vertical slots 33 (Fig. 1)for the reception of the upper ends of the turnbuckle type ball bearingsupporting members indicated generally at .34 which are attached theretoby bolts 35. Members 34 may be commercially available, self-aligningbearing rods. The lower balls of members 34 are attached to the end lugs35 of lapping head 24 by bolts 31 which engage with internal threads inthe balls. Within limits, this flexible supporting arrangement maintainsor efiects the free vertical, horizontal and transverse movement oflapping head 24, while always maintaining its longitudinal axis parallelto the axis of rotation of the work 9, the upper and lower balls ofmembers 34 being restrained against movement but their mating bearingparts being freely movable It is preferred that the relative speed be- 4with respect to the balls, to facilitate the threedimensional movement.

Referring to Figures 3, 4 and 6, the front side of lapping head 24 isprovided with a recessed seat for the reception of a self-aligningantifriction bearing 38 which incorporates an integral sleeve element39. The bore of 39 is sufficiently large to accommodate the crank end 40of the double eccentric with a sliding fit, so that head 24 is free tomove axially with respect to the double eccentric during operation ofthe latter. In setting up the machine, a clearance of about 1%" minimumis preferably allowed between the end of 40 and the adjacent side of theworking face of the head, so that the lapping elements of the head willalways conform to the profile of the work as the head is oscillated bythe double eccentric. Head 24 is also provided with two selfaligningbearing receiving recesses 24a located approximately one-fourth of thedistance in from each end of the head for the loose reception of thehemispherical heads of spring-actuated, force-applying members 42. Therear ends of members 42 are threaded to receive adjusting nuts 43 whichbear on the rear ends of compression springs 44, the forward ends ofwhich abut backing members 19. Thus, the force exerted by the springs 44against head 24 can be increased by turning nuts 43 in a forwarddirection or decreased by adjustment in the opposite direction tomaintain any desired contacting pressure of head 24 against work 9. Theforward ends of members 42 are steadied loosely within holes in members[9, a total clearance of the order of about 1% being allowed, so thatthe hemispherical heads of members 42, seating in recesses 24a aremaintained free to assume a position on the same horizontal line as thecenter of crank end 40 during its rotation, thereby avoiding thedevelopment of force couples which would tend to throw the longitudinalaxis of lapping head 24 out of parallelism with the longitudinal axis ofthe work 9. The forward ends of members 42 may be freely slidable withinthe holes in members H), as shown in Figure 1, or may be provided withconventional latching devices for complete longitudinal retraction fromhead 24 for'facility of adjustment.

It will be seen, therefore, that with the selfaligning means suspendedas indicated, with the ends of force-applying members 42 bearing againstthe head 24 in recesses 24a and in parallel relation with force-applyingmember 44 of double eccentric 23 also bearing against head 24, to effectthree-dimensional movement of said head, lapping head 24 is therebymaintained in position to produce substantially free movement along eachof the three principal reference axes of elements 42, 40, 42, whilemaintaining the longitudinal elements of the lapping head parallel tothe axis of rotation of the object being surfaced, as heretoforedescribed;

In the assembly arrangement of the several parts of the machine, it ispreferred to dispose the points of connection of the lower balls ofmembers 34 with head 24, the center of rotation of bearings 38, and theself-aligning-bearings 24a in head 24 receiving the ends offorce-applying members 42 all on a common horizontal line passingthrough the center of gravity of head 24. With this organization, thedevelopment of inertla force couples which impose nonuniform loads onthe work at the top and bottomof the oscillation cyles isavoided.

Referring to Figures 4 and5, the anti-friction bearing retainers 45 and46 of front bearing 2!: and rear bearing 22, respectively, rotatablysupport the outer 23 of the eccentric drive for head 24. The bore ofshaft 23 is provided with the greater eccentricity of the pair ofeccentrics constituting the drive, the degree of eccentricity of thebore of 23 being chosen so that the maximum radius of oscillatorymovement to be applied for lapping head 24 will be produced when theeccentricity of the second member of the pair is added, while theminimum radius of oscillatory movement to be applied will be producedwhen the two ecoentricities are opposed to one another. In practice, aneccentricity of 3 for the bore of shaft 23 has proved entirelysatisfactory. inner shaft 4! is supported in freely rotatablerelationship within the bore of 23 by the two end bearing bushings 48and 49-. The second eccenti'icit'y of the drive is provided by theoffset of crank: end 40 of shaft 41, which, for the typical casedescribed, may be 3 Shaft 23 is turned at a relatively high speed byV-belt sheave 59 fixedly secured thereto by set screw 5|. Shaft 41 isturned at a slow rate with respect to shaft 23 by V-belt sheave 52secured to collar 53 by one or more screws 54, collar 53 being mountedin freely rotatable relationship on the outside of shaft 23. To securethe differential speed necessary to turn 41 at a constant rate withrespect to 23, the diameter of sheave 52 is made slightly greater thanthe diameter of sheave 50, a difference of about referred to pitchdiameter sheaves operating with ordinary belt slippage resulting in alag of one complete revolution of shaft 41 with respect to shaft 23 onceevery two minutes when shaft 23 is revolved at 600 R. P. M. Sheaves 50and 52 are driven from a common V-belt pulley 55, secured to the shaftof motor 56, through V belts 51 and 58, respectively'. Drivingconnection between sheave 52 and shaft 41 is accomplished through collar59 provided with crank pin fill which engages with a radial slot 6!formed in the forward face of collar 53. Collar 59 is fixedly secured toshaft 41, in slidable relationship with the forward end of shaft 23, bydrive pin 62, collar 59 thus securing sheave 52 against outward movementalong shaft 23. The opposite end of shaft 41 is provided with with acounterweight 63 fixedly attached to shaft 4'! in slidable relationshipwith the adjacent end of shaft 23 by set screws or any other suitablemeans, not shown. It will be understood that counterweight 63 isproportioned and mounted so that its unbalanced mass will oppose andcounteract the unbalanced forces produced by the complex movement oflapping head 24. The double eccentric mechanism hereinabove describedcauses a point on the lapping head to describe a high non-repetitivepath, the diameter of the lapping circle varying continuously from aboutk" to 1" every two minute for the specific conditions detailed. It willbe understood that the paths described by individual abrasive particlesbetween the working surface of head 24 and the worked surface ofcylinder 9 are even more random and complicated due to the superaddedcontinuous rotation of the work 9 within bearings 5.

The foregoing is a highly important feature of this invention, and thispattern of movement makes it possible to eliminate pits or depressionsfrom the surface of the work without concurrently cutting grooves, orso-called comet tails, transverse the lower peripheral edges of thedepressions. The pits or depressions referred 6 to are sometimescylindrical in form. with their axes normal to the work, while at othertimes they may be concave or more or less conical in shape, andapparently are caused by non uni form deposition of metal, or theinclusion or minute gas bubbles, where the surface of shell in iselectroplated, as is the usual practice. In the course of lapping,abrasive particles collect within these depressions and, as thesurrotmding' metal is abraded away, and eventually forced out by thelapping head. The paths taken by these escaping particles have animportant bearing on the formation of comet tails. If the movement ofthe lapping head is pure reciprocatory and the work is simultaneouslyturned, the lower edges of the depressions are grooved out between linesgenerally defining a sector having a center coinciding with the centerof the depression. The continually expanding and contracting oscillatorypattern imparted to the lapping head 5y the double eccentric mechanismhereinabo've do scribed appears to remove abrasive particles from thepits by a rotational or cratering movement, urging the particles alongpaths distributed around the full peripheries of the pits and morenearly concentric therewith. The result is that the formation of thecomet tail defects is ractically completely avoided and the surfacequality greatly improved.

The rough lapping head shown in Figures 4 and 7 and the fine lappinghead shown in Figures 6 and 8, are identical in all respects, except asregards the working elements and thei'nanne'r in which these elementsare attached to the heads, and are completely interchangeable in theirmounting on the machine. The rough lapping head elements consist ofstraight lengths of tool steel or other hard material 64, slightlylonger than the width of work 9, seated "within recesses in the head 24and retained in place'by socket-headed bolts 65. The working surface ofstrips 64 are shaped to a curvature conforming to the periphery of shellIll, the surface of which it is desired to lap. For best results, it ispreferred to limit the length of elements to the.

length of the cylindrical work piece plus about twothirds of the lengthof the maximum stroke of crank 40, thus compensating for excessive edgelapping effects byre'stricting lapping action in the end zones to only aportion of each cycle of oscillation. The width ofelements 64 should belimited to values where the total pressures applied to the worked areaare not so great as to deflect the work to such a degree thatdimensiohal control is lost Excessively wide elements also develop onwedges between their working surfaces and the work, which reducescutting eificiehcy, since the oil film then attains a thickness greaterthan about two-thirds the average abrasive particle diameter and theparticle are thereby cushioned from effective contact with the work. Inthe typical case where a 24" diaiheter roll of 24" face widthwassu'i'faced ac cording to this invention, elements 64 havinga width.of 1 2" and a length of 24%;," with center-to-centr spacing of about 29proved entirely satisfactory. v

The fine lapping element consists of a full tetrafiuoroethylene, such asthat disclosed in my copendingapplicatioh, Ser. No. 163,562, filed May22, 1950. The fine lap is secured to the working face of head bymetalretaining stripsiil attached to the rearwardly inclined edges of 24with cap screws 68. It will be understood that, if springs 44 areregulated to the same compression as during the rough lapping operation,the total pressure applied to the work during fine lapping will remainunchanged; however, the pressure per unit area will be reduced in thedirect proportion in which the working area of the fine lap exceeds thecombined working areas of the two strips 64. The length of the finelapping'element is preferably limited to the width of the work plusabout two-thirds the maximum stroke of crank 40, as hereinabovedescribed for the rough lapping elements, to compensate for the somewhatmore rapid lapping which occurs in the end zone regions.

The fine lapping element 66 is backed with a relatively thin canvas bag69 filled to a thickness of about to /2" with pitch or a material ofsimilar properties, the pitch having a plasticity at operatingtemperatures and pressures sufficient to permit strip 66 to conform tothe surface of shell l0, while still providing support for the strip anddistributing pressure evenly over its entire area. 'The pitch backingbag is secured in place on head 24 by tucking the loose edges beneathretaining strips 61 and punching holes through the edges for the passageof screws 68.

Where an impervious material, such as polytetrafluoroethylene, isemployed as the fine lap,

the working surface of strip 65 is preferably broken with a uniformsquare pattern of slit lines having a depth of 0.040" to 0.060", asindicated at in Fig. 8, each unit of which measures about 0.015" toabout 0.125" on a side, with one diagonal'of the square approximatelyparallel to the axis of head 24 and work 9. It will be understood thatthe lap is not weakened appreciably by the surface roughening impartedby the slitting, and a polytetrafluoroethylene lap thick may be treatedas described without sacrificing much of its useful strength. Theprimary purpose of the slit lines is to relieve pressure built up in theabrasive-suspending liquid vehicle film, particularly when very fineabrasives such as diamond dust are employed, so that the thickness ofthe liquid film will not exceed a value ofabout twothirds the averageabrasive particle diameter, where abrading action is considerablyreduced or even entirely halted, An additional effect of surfaceslitting is that the flexibility of the lap isthereby somewhat improved,so that the formation of hard spots resulting from non-homogeneities inthe lap material is largely avoided.

H In operation, the full face width'of the work is lapped by applyingsuspensions of abrasive of progressively decreasing particle size insequence to the surface to be worked. This may be accomplished by eitherdripping the suspensions on the work at a point above the lapping head,or applying the suspensions manually with a paint brush. The work may beturned in either direction as viewed in Fig. 1; however, it is pre-'ferred to operate with counterclockwise movement, for the reason thatthe recovery of suspended abrasive escaping from the edges of the workis thereby somewhat facilitated. The compressions of the springs 44 areadjusted so that an average contacting pressure of below about 18lbs/sq. in., preferably about 10 lbs/sq. is applied by the head to thework. The lapping is accomplished in two stages, the rough lapping beingeffected at a relatively rapid rate by the tool steel head after whichthe fine lapping head is substituted, and the fine lapping conducted ata somewhat slower rate until the final quality of finish is obtained. Itis preferred to reverse the direction of oscillation of the lappingveniently accomplished by providing the apparatus with a conventionalreversible type motor 56 for driving the double eccentric mechanism.

It will be apparent from the foregoing dis-- closure in detail that thisinvention may be modified in various ways including the manner in whichthe lapping heads are supported, andpressed against the work andoscillated, without departing from the scope and spirit of theinvention; it is not the intention to be limited in the scsope of thedisclosure except to the extent indicated in the following patentclaims.

I claim:

1. In a lapping mechanism including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, a lap-'ping head having a con-cave surface to conform substantially to theexternal surface of the cy1in-' drical work to be surfaced, supportingmeans for maintaining the lapping head in parallel relation andsubstantially in the same horizontal plane with the axis of the workpiece, said supporting means comprising upright supporting membersmounted in spaced relationon the base structure,

shaft having its ends rotatably journaled insaid upright members andpositioned substantially in spaced, parallel relation with the lappinghead, hanger arms supported at one end on said shaft with the other endsfree, self-aligning supporting means depending from the free ends ofsaid hanger arms and engaging the outer ends of the lapping head forsupporting the lapping head parallel with the axis of the work,-

eccentrically operated means also mounted on the base structure foroscillating the lapping head, and auxiliary means positioned in spacedrods for producing vertical, horizontal and trans-, verse movement ofthe lapping head, in parallel relation to the axis of rotation of thework piece, eccentrically operated means positioned to oscillatethelapping head against a rotating cylindrical object, powered means foroscillating the lapping'head past the surface of a rotating cy-.lindrical object, and a self-aligning connection.

between the powered means and the lapping head for controlling theoscillations.

3. The invention of claim 2 in which the eccentrically operated meanscomprises an inner shaft, and an outer shaft having a bore with greatereccentricity than the inner shaft, an offset crank end on the innershaft for producing the second eccentricity of the drive, and acounterweight mounted on the inner shaft having an unbalanced massopposing and counteracting the acumen 9 unbalanced forces produced bythe complex movements of the lapping head.

4. The invention of claim 2 in which the eccentric drive comprises adouble eccentric in-- cluding an inner shaft and an outer shaft andfront and rear bearings for rotatably supporting the outer shaf, saidouter shaft having a bore with greater eccentricity of the pair ofeccentrics constituting the drive, while the inner shaft is supported inrotatable relationship within the bore of the outer shaft, so that themaximum radius of oscillatory movement for the lapping head is producedwhen the second member of the pair is added, while the minimum radius ofoscillatory movement is produced when the two eccentrics are opposed toone another.

5. The lapping machine of claim 2 in which the powered means foroscillating the lapping head past the surface of the object to be lappedcomprises a first rotatable shaft having an eccentric bore, a secondshaft mounted in substantially free, independent, rotatable relationshipwithin the eccentric bore of said first shaft, said second shaft havingan eccentrically disposed pin forming a longitudinal extension of saidsecond shaft and positioned for oscillating said lapping head wheneccentrically operated, means eliminating relative movement between saidshafts in a direction parallel to the axes of said shafts, a firstpowered means for turning said first shaft at one predetermined speed, asecond powered means mounted in independent, rotatable relationship tosaid first powered means for turning said second shaft at apredetermined speed differing from the speed of said first shaft, saidsecond powered means having a driving slot, a collar carried by saidsecond shaft and freely movable with respect to said first shaft, saidcollar having an eccentrically disposed driving pin for engagement withsaid driving slot of said second powered means, a common powered meansfor driving said first and second powered means, and a self-aligningconnection positioned to move axially with respect to the longitudinal,eccentrically disposed pin of said second shaft and in engagement withsaid pin.

:6. In :a lapping apparatus including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, a lappinghead having a concave surface to conform substantially to the externalsurface of the cylindrical Work to be surfaced, means for dependentlysupporting the lapping head in working position'comprising uprightmembers in spaced relation mounted on said base, an oscillating shaftrotatably journaled in said fupright members, hanger arms supported atone end by said shaft with their opposite ends free, supporting meansdependent from the free ends of said arms and engaging opposite ends ofthe lapping head to support the lapping head in parallel relation withthe work to be surfaced, powered mean for oscillating the lapping headpast the surface of the cylindrical object to be surface, aself-aligning connection between the aforesaid ,powered means and thelapping head, and a pair of force applying means in spaced parallelrelation with said oscillating means and with each other, positioned tourge the lapping head in the direction of the axis of the work to besurfaced during said oscillations.

'7. The invention of claim 6 in which the supporting means dependingfrom the hanger arms comprises self-aligning bearing rods with one setof elements at one end attached to the hanger 10 members and thecorresponding movable ele-' ments at the opposite end afiixed in spacedrelation to the lapping head.

8. The lapping mechanism of claim '6 in which the centers of thedependent supporting means, the ends of the force applying members, thecenter of rotation of the self-aligning connection between the poweredmeans oscillating the lapping head and the lapping head, and the centerof gravity of said lapping head, when placed in operation for surfacinga cylindrical work piece, are all positioned to be maintainedsubstantially upon a common horizontal line parallel to a line drawnthrough the axis of rotation of the cylinder to be surfaced.

9. In a lapping apparatus including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, a lappinghead having a concave-curved working surface to conform substantially tothe external surface of the cylindrical object to be surfaced, and inparallel relation therewith, an eccentric driving means positioned foroscillating the lapping head at its center portion, means to urge thehead to-- ward the axes of the cylindrical Work piece, .supporting meanseffecting vertical, horizontal and transverse movement of the lappinghead while maintaining the longitudinal axis of said head parallel tothe axis of rotation of the work piece, comprising self-aligning bearingrods which in combination with said driving means constitute threeprincipal references axes with substantially free movement of saidlapping head along each of said axes to produce three-dimensionalmovement of the lapping head during oscillation while still retaininglongitudinal elements of said head in parallel position to the axis ofthe cylindrical object when rotated.

10. In a lapping apparatus including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, arotatable shaft supported on said base structure, hanger arms in spacedrelation having one end of each supported on said shaft with their freeends in position to support a lapping head, a lapping head dependentlysupported by the free ends of said arms, a. double eccentric means foroscillating the lapping head axially with respect to the eccentricmeans, comprising an inner shaft and an outer shaft, a crank end on theinner shaft and a sleeve bearing mounted on the lapping head foraccommodating the crank end, powered means for driving each of saidshafts at different speeds to oscillate the lapping head, force applyingmeans mounted on said base structure in parallel relation and onopposite sides of the double eccentric with their ends bearing againstthe lapping head in self-aligning relationship to urge the lapping headtowards the axis of the cylindrical work piece.

11. In a lapping apparatus including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, amechanically actuated, self-aligning lapping head having aconcave-curved surface to conform to the cylindrical surface of the workpiece, a double eccentric driving means positioned to operate thelapping head comprising an inner shaft and an outer shaft mounted to bedriven at different speeds, spaced bearingssupporting said double eccentc a freely rotatable shaft supported at right angles but in spacedrelation to the eccentric driving means, hanger arms extendinghorizontally from said rotatable shaft and supporting said lapping head,means positioned to maintain the lapping 1 1 head against thecylindrical work piece including a crank end of the double eccentric inposition to oscillate the lapping head, spring-actuated, force-applyingmeans in spaced parallel relation with said eccentrically operatedshafts, positioned to urge the lapping head toward the axis of the workpiece, and self-adjusting means depending from said hanger arms capableof maintaining said force-applying means and lapping head incoordinating relationship.

12. In a lapping apparatus including means for rotatably supporting anddrivingly rotating a cylindrical work piece, a base structure, amechanically actuated, self-aligning lapping head mounted on said basehaving a concave-curved surface adapted to conform to the cylindricalsurface of the work piece, a rotatable shaft supported by said base inspaced parallel relation to the lapping head, hanger arms extendinghorizontally from said rotatable shaft and positioned to support saidlapping head, a double eccentric driving means for oscillating thelapping head comprising an inner shaft and an outer shaft, powered meanspositioned to drive each of said shafts, with one at a speed differingfrom the other, a pair of spaced bearings supporting said doubleeccentric, a counterweight mounted on the inner shaft at the endopposite to the driving means, having an unbalanced mass opposing andcounteracting unbalanced forces produced by the complex movement of thelapping head, means for maintaining the lapping head in lapping positioncomprising a self-aligning bearing in the lapping head, and a crank endof the double eccentric positioned therein to apply oscillating actionthereto, spring-actuated means in parallel relation with saideccentrically operated shafts and positioned to urge the head in thedirection of the axis of the work piece, with one end of each shaftbearing against said lapping head in self-aligning relationship, andselfadjusting means dependent from said hanger arms for maintaining thelapping head in oscillating position.

13. The method of lapping a cylindrical work piece of substantialdimensions comprising rotatably supporting and drivingly rotating thecylindrical work piece while dependently supporting a lapping head inhorizontal, parallel relation therewith having a surface adapted toconform to the surface of the cylindrical work piece, applying doubleeccentric action to the lappinghead while urging the lapping headtowards the axes of rotation of the cylindrical object by forces inspaced, parallel relation with and independent of the eccentricmovement, and moving the lapping head in vertical, horizontal andtransverse directions with respect to the cylindrical object whilemaintaining the longitudinal elements of the lapping head parallel tothe axis of rotation of the cylindrical object.

14. The method of claim 13 in which two independent eccentric movementsof differing ro tational speed are applied simultaneously to the lappinghead to oscillate the lapping head past the surface of the work to belapped, and produce the maximum radius of oscillatory movement of saidlapping head when the eccentricities of saidtwo movements are added, andproducing the minimum radius of oscillatory movement when theeccentricities of said two movements are opposed.

15. In the lapping of cylindrical objects of substantial dimensions,rotatably supported and drivingly rotated, in which a suspension ofparticulate abrasives in liquid vehicle is applied to the surface of thecylindrical object and to the lap of a lapping head dependentlysupported in horizontal, parallel relation with the axis of thecylindrical object and in position to provide vertical, horizontal andtransverse movement of the lapping head while maintaining thelongitudinal axis of the head parallel to the axis of rotation of thecylindrical work piece, the steps comprising oscillating the lappinghead by a pair of eccentric movements applied to the head while itssurface is maintained in conformity with the profile of the cylindricalwork surface, and urging the head in the direction of the axis of thecylindrical work piece by forces parallel to each other and independentof and parallel with the pair of eccentric movements and maintaining thecenters of application of the parallel forces and the point ofapplication of the pair of eccentric movements in a common horizontalplane to eliminate development of force couples tending to throw thelongitudinal axis of the lapping head out of parallelism with thelongitudinal axis of the cylindrical work piece.

16. The invention of claim 15 in which one of the pair of eccentricmovements is greater than the other so that the maximum radius ofoscillatory movement applied to the lapping head is produced when theeccentricity of the second movement is added, while the minimum radiusof oscillatory movement is produced when the two eccentric movements areopposed to one another.

17. The invention of claim 15 in which different speeds are applied toeach of the pair of eccentric movements, while counterweighting one ofthe eccentric movements to counteract the unbalanced forces produced bythe complex movement of the lapping head during oscillation by the pairof eccentric movements and the superadded continuous rotation of thecylindrical work piece, to cause a point on the lapping head to describea highly non-repetitive path to eliminate surface irregularities fromthe work surface.

THOMAS G. LEWIS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 512,012 Delano Jan. 2, 1894 960,188 Nichols May 31, 19101,039,514 Gladhill Sept. 24, 1912 1,142,146 Combs June 8, 1915 1,227,775Friess May 29, 1917 1,316,506 Pitter Sept. 16, 1919 1,593,212 Hart July20, 1926 2,195,047 Wallace Mar. 26, 1940 2,195,049 Wallace Mar. 26, 19402,195,053 Wallace Mar. 26, 1940 2,195,065 Wallace Mar. 26, 19402,402,340 Parmenter June 18, 1946 FOREIGN PATENTS Number Country Date220,986 Germany Apr. 14, 1910 393,668 Germany Apr. 5, 1924

